THANK YOU SO MUCH, WAYNE!
You're right: I was using the two TH subs like a sort of Geddes style multiple subs...
The problem is that the Minidsp Flex has only 4 balanced outputs, so I will need to keep only two flanking subs and discard the two "Geddes" TH I already have...
I hope that the flanking ones will give me a better result than the other two...
Only one question: is it possible to change the position of the vent, if needed?
Thank you very much again!!!